It is well known that if the engine check light is on, this indicates the occurrence of various failures and malfunctions that can be associated with both the internal combustion engine itself and its systems. At the same time, quite often during computer diagnostics errors related to the engine power system and the quality of mixture formation are identified.
In fact, in some cases the error “0171 mixture too lean” is read. It is not difficult to guess that a lean mixture indicates an insufficient amount of fuel in the working mixture or indicates an excess of air. Next, we will take a closer look at what a lean mixture is and why error p0171 occurs, as well as what to do in this case and how to fix the problem.
Check engine light on: P0171 error
Let's start with the fact that the injection engine is not only controlled by an ECU, but is also equipped with a self-diagnosis system. In turn, the system is capable of recording malfunctions and failures, and then recording them in the controller’s memory. In this case, errors are recorded in the form of a code. In fact, when scanning you can read the code: error p0172, p0170, p0174, etc.
So, each of the codes has its own decoding. In this case, the p0171 error occurs quite often. This code indicates that there are malfunctions in the mixture formation process; the mixture entering the engine is too lean.
Such problems with the fuel assembly (fuel-air mixture) for a Euro-2, EURO-3 and higher engine mean that there is 30% more air in the fuel-air mixture compared to the optimal amount.
If such an error occurs, the following indirect signs also indicate a lean mixture:
- the engine is difficult to start;
- engine idling is disrupted;
- engine power lost;
- speed gain and acceleration are worse;
- increased fuel consumption;
- popping noises appeared in the exhaust system;
When the ECU detects a problem, the “check engine” light comes on on the instrument panel. It is important to understand that driving with a lean mixture is strongly not recommended, as this can lead to serious damage to the internal combustion engine and other systems. The main reason is a violation of the temperature regime, that is, banal overheating, burnout of valves, cylinder head gaskets, etc.
What You Need to Know About Lean Fuel Codes P0171 and P0174
Difference Between Trouble Codes P0171 and P0174
Essentially, the P0171 code indicates “bank 1,” which is the side of the engine with cylinder number one, while P0174 indicates the cylinders on the other side of a V6 or V8 engine.
If your engine has four or six cylinders (that is, all on one side of the engine), you will most likely receive a P0171 code. However, on some newer vehicle models, the computer treats the engine as two separate banks when generating codes, even if it is set to line. For example, in a four-cylinder engine, bank 1 represents cylinders one and two, and bank 2 represents cylinders three and four.
If you need more information about a specific model, consult your vehicle's repair manual.
What if I have other codes?
Often a P0171 or P0174 code will be accompanied by a P0300 random misfire trouble code. In this case, focus on code P0171 or P074 as they are the most likely cause of a random engine misfire.
If your computer has codes P0171 and P0174, focus on those components that affect all cylinders, such as the MAF sensor, clogged fuel filter, or problems with the fuel pressure regulator. Otherwise, concentrate on the side of the engine indicated by your DTC.
Just keep in mind that MAF sensor problems will sometimes cause one code even if they affect all cylinders.
Causes of a “lean” mixture
Having dealt with the risks that may arise when error P0171 appears, you need to move on to the causes of the problem.
As mentioned above, fuel assembly depletion can occur for two reasons:
- Too little fuel enters the cylinders;
- Too much air is supplied;
Lack of fuel and/or excess air can lead to different problems. In the case of air, you should immediately check the mass air flow sensor, as its failures will lead to incorrect readings. The sensor may be either faulty or dirty.
More excess air can enter the intake through the EGR valve. If the valve does not close tightly enough, exhaust gases continually fall into the intake. Also, other causes of air leaks into the intake should not be ruled out.
For insufficient fuel, the fuel pump is checked first. If the pump does not produce the required pressure, the reason is obvious. The next element is the fuel injectors. Their malfunction or contamination also causes insufficient fuel supply in a certain unit of time.
You should also pay attention to the fuel filter. It also happens that the pump and injectors are in order, but fuel is not supplied in the required volume. Fuel may also partially flow out in the area of the pressure regulator without entering the combustion chamber.
As you can see, there are really many reasons. It turns out that to eliminate the causes of error P0171, a comprehensive diagnosis of the ECM, as well as the engine power system, is necessary.
Problems with the oxygen sensor
If your computer has triggered a trouble code for a possible faulty oxygen sensor along with other codes, check these and other codes first. Often problems in other areas will affect the O2 sensor readings.
An exhaust leak can also affect the sensor output.
But it is true that oxygen sensors can also fail. Testing can help you check the working condition of the sensor.
A quick way to check the sensor is to replace the sensors if your car has more than one. If the problem persists in the same location, you know the sensor is working fine and the problem is somewhere else: possibly a vacuum or an exhaust leak.
When checking the O2 sensor, visually inspect it for possible contamination.
High mileage engines can suffer from serious mechanical problems that can cause code P0171 or P0174 among other problems.
Engine diagnostics with a lean mixture
First of all, when diagnosing, you need to accurately determine that there are no other errors besides error P0171. For example, if P0134 is also detected, indicating that there is no signal from the oxygen sensor, you first need to deal with this problem.
As practice shows, when analyzing errors it is necessary to pay attention to cause-and-effect relationships. If, for example, the lambda probe is faulty, then replacing it or another available solution to the problem often allows the mixture formation to be normalized, that is, to remove the P0171 error.
However, if there is only a P0171 code, you should look for the cause of excess air or low fuel flow. Usually they start with cleaning and diagnosing the air flow sensor. The fact is that the error often occurs because the air flow meter is dirty.
In this case, it is enough to clean the sensitive elements, after which, based on the correct readings, the ECU will adjust the composition of the mixture. It also happens that the air sensor itself is clean, but its contacts are dirty. In this case, you need to clean the contacts of the mass air flow sensor. Carbicleaner or other suitable cleaners are suitable for cleaning.
If everything is fine with the sensor, you need to check the system for leaks (vacuum leaks). To do this, you need to check the inlet pipe, the throttle body (THB) outlet, the THB body gasket, the manifold gaskets, and the connection between the vacuum hose and the intake manifold.
We also recommend reading the article on how to remove air from the cooling system of a car engine. From this article you will learn about the reasons why the cooling system becomes airy, as well as how to remove the air lock in the cooling system.
At the same time, they check the crankcase ventilation system hose, adsorber elements, installation locations of plugs on the intake manifold, etc. The exhaust system, where the oxygen sensor is located, also deserves special attention. The installation location of the oxygen sensor must be sealed, otherwise the sensor will supply incorrect values to the ECU. It would also be a good idea to check the pressure difference sensor in the EGR system.
If a car has such a system, usually by 80-100 thousand km. mileage, the entire complex of components of the exhaust gas recirculation system needs to be checked. Let us also add that if the ECM sensors are the culprits of the failures, they are often replaced with new ones, since cleaning does not always give results.
If we talk about the fuel system, diagnostics often begin with the injectors. Injector nozzles need to be cleaned (injector cleaning) on a special stand. At the same time, they check the operation of the fuel pump, measure the pressure in the fuel rail (fuel rail), etc.
As part of troubleshooting, an auto scanner is actively used, thanks to which it is possible to more accurately determine the problematic element of the system. Finally, let’s add that sometimes error P0171 appears and disappears, that is, the problem is floating. So, in this case, the culprit is often the contacts between the sensor and the ECU. In this case, all connections must be checked.
Using the Scan Tool
Trouble code P0171 or P0174 can be caused by a vacuum leak or a faulty sensor. Vacuum leak errors usually—not always—show up faster at lower speeds; like rough idle, for example.
Problems are more common at high engine speeds. Problems at high speeds are often caused by a faulty sensor or problem in the fuel system, including the MAF sensor, engine coolant temperature (ECT), throttle position (TPS), barometric pressure sensor, or others that monitor fuel delivery.
A capable scan tool can check fuel trim values at idle and at higher engine speeds and determine when leaning occurs. This may help find problems.
If your computer has other trouble codes that point to one or more sensors, check those first. These may be the cause of codes P0171 or P0174.
If you receive a code for the oxygen sensor, this may or may not be the cause of the problem; More often than not, other sensors are the problem. Therefore, you may want to check other components before testing and replacing the O2 sensor.
Let's sum it up
Taking into account the above information, it becomes clear that error P0171 can occur either separately or in combination with other errors recorded in the ECU memory. In any case, you first need computer diagnostics of the engine and decoding of all errors.
If no causes are found or the P0171 error is the only one on the list of problems after diagnosis, then it is necessary to check the systems and elements discussed in this article.
We also recommend reading the article on how to clean injection nozzles. In this article, you will learn about the available methods for cleaning injectors, as well as what you need to consider when choosing a cleaning method.
As a summary, we note that a lean mixture is dangerous for a car engine, that is, the problem cannot be ignored. Otherwise, further operation of the vehicle will lead to the fact that the power unit itself, as well as other elements and systems, may require repair.
To avoid possible consequences, it is necessary to regularly clean and check the EGR system (if equipped), as well as read and decipher errors in the ECU memory at certain intervals (even if the “check” is not lit). This approach will make it possible to timely identify failures and malfunctions at the initial stage, which eliminates prolonged operation of the internal combustion engine on a lean mixture.
Model-Specific Issues
If you are having trouble finding the cause of the code(s), then the problem may lie with a specific component specific to your vehicle model. Consult your vehicle's repair manual.
If you don't have a manual for your model, you can buy a relatively inexpensive aftermarket manual from Amazon. Not only can Haynes manuals help you locate components in your vehicle, but they also provide step-by-step procedures for many maintenance, repair and troubleshooting projects you can do at home. This way, you can save thousands of dollars a year on many simple maintenance and repair tasks that you can do right at home.
FINE. Let's look at the most common problems so you can diagnose the cause of the problem in your engine.
A MAF sensor with a dirty sensor element may throw a P0171 code.
Preventing Damage from DTCs P0171 and P0174
The problems that cause trouble codes P0171 and P0174 can not only impair engine performance, but also damage other components over time. They can damage the catalytic converter.
A simple job like cleaning the MAF sensor or replacing a clogged fuel filter can solve your problem. But ignoring the problem can lead to costly repairs later.
It is cheaper to clean the sensor or replace the filter than to replace the catalytic converter and replace other damaged components.
So follow this guide and start checking for the most common problems that cause trouble codes P0171 and P0174.
